Accessory device, imaging apparatus, and communication control program

ABSTRACT

An imaging apparatus that provides, between itself and an accessory device, a notification channel used for notification from the imaging apparatus to the accessory device, a first data communication channel used in data transmission from the accessory device to the imaging apparatus, and a second data communication channel used in data transmission from the imaging apparatus to the accessory device. An accessory control unit transmits data via the first data communication channel in response to having received a transmission request signal via the notification channel, and selectively adds, to the data, a communication standby request for keeping a transmission request signal from being transmitted from the imaging apparatus to the accessory device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No. 16/144,897, filed Sep. 27, 2018, which is a continuation of International Patent Application No. PCT/JP2017/012368, filed Mar. 27, 2017, which claims priority to Japanese Patent Application No. 2016-072984, filed Mar. 31, 2016, all of which are hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to an imaging apparatus, and an accessory device such as an interchangeable lens or the like, which are communicable with each other.

BACKGROUND ART

There are known lens-replacement type camera systems where an imaging apparatus, which is the camera main body, performs imaging processing and lens control, and lens devices which are interchangeable lenses perform lens driving in accordance with control commands from the camera main body. In such camera systems, transmission of control commands from the camera main body to the interchangeable lens, and transmission of lens information from the interchangeable lens to the camera main body, are performed via a communication channel for exchanging information with each other.

Of such lens-replacement type camera systems, digital camera systems in particular require smooth lens control in accordance with imaging cycles when shooting moving images or taking live view images. Accordingly, the imaging timing of the camera main body and the control timing of the interchangeable lens need to be synchronized, and the camera main body needs to complete obtaining of lens information necessary for lens control and transmission of control commands to the interchangeable lens within an imaging cycle.

On the other hand, advanced imaging technology has led to increase in the data amount of lens information that the camera main body obtains from the interchangeable lens, and frame rates are faster. Accordingly, there is need to communicate great amounts of data in a shorter time than conventionally.

PTL 1 discloses a clock-synchronized communication system made up of three channels, which are a clock channel, a data transmission channel from the camera main body to the interchangeable lens, and a data transmission channel from the interchangeable lens to the camera main body. In this communication system, the camera main body serves as a communication master to generate clock signals, and outputs one frame of clock signals to the interchangeable lens via the clock channel. Thereafter, the input and output of the clock channel are switched, and the interchangeable lens that is the communication master instead of the camera main body outputs a transmission standby request to the same channel. Accordingly, the interchangeable lens can notify the camera main body that it is in a processing standby state after communication.

CITATION LIST Patent Literature

PTL 1 Japanese Patent Laid-Open No. 9-304804

According to the communication system disclosed in PTL 1, the communication master needs to be switched by time management between the camera main body that outputs clock signals and the interchangeable lens that outputs communication standby requests over the same channel. Accordingly, there is a need to provide time for switching the communication master in order to prevent collision of communication, i.e., a communication-invalid time during which communication cannot be performed, which as a result may lead to delay in communication and control.

Stopping output of communication standby request signals to the clock channel by the interchangeable lens to solve this problem results in the interchangeable lens not being able to make communication standby requests to the camera main body at all. If large amounts of data are communicated without outputting communication standby request signals, there is a concern of communication breakdown occurring in cases where a reception buffer overflow occurs at the interchangeable lens that is the communication slave, or where data to be transmitted to the camera main body is not generated in time. Also, providing a new channel to output communication standby request signals increases electric power consumption, and reduction in size of the camera main body and interchangeable lens is inhibited.

It is an object of the present invention to realize an accessory device and imaging apparatus capable of performing high-speed data exchange without leading to breakdown of communication, without adding new channels.

SUMMARY OF INVENTION

An accessory device according to the present invention is an accessory device detachably mounted to an imaging apparatus, having an accessory communication unit that provides, between itself and the imaging apparatus, three channels made up of a notification channel used for notification from the imaging apparatus to the accessory device, a first data communication channel used in data transmission from the accessory device to the imaging apparatus, and a second data communication channel used in data transmission from the imaging apparatus to the accessory device, and an accessory control unit that performs control of the accessory communication unit. The accessory control unit transmits data to the imaging apparatus via the first data communication channel, in accordance with having received a transmission request signal via the notification channel. The accessory control unit selectively adds, to data to be transmitted to the imaging apparatus, a communication standby request for keeping the transmission request signal from being transmitted from the imaging apparatus to the accessory device.

An imaging apparatus according to the present invention is an imaging apparatus to which an accessory device is detachably mounted, having an camera communication unit that provides, between itself and the accessory device, three channels made up of a notification channel used for transmission of a transmission request signal from the imaging apparatus to the accessory device, a first data communication channel used in data transmission from the accessory device to the imaging apparatus, and a second data communication channel used in data transmission from the imaging apparatus to the accessory device, and a camera control unit that performs control of the camera communication unit. The camera control unit stops transmission of the transmission request signal while receiving, from the accessory device via the first data communication channel, a communication standby request to keep the transmission request signal from being transmitted.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating the configuration of a camera system including an imaging apparatus and an accessory device according to the present invention.

FIG. 2 is a schematic diagram illustrating communication circuits between the imaging apparatus and accessory device.

FIGS. 3A through 3C are schematic diagrams illustrating communication waveforms in a communication mode M1.

FIG. 4 is a schematic diagram illustrating communication waveforms in a communication mode M2.

FIGS. 5A through 5C are schematic diagrams illustrating communication waveforms in a communication mode M3.

FIG. 6 is a flowchart for describing a flow for deciding a communication format at the accessory device and imaging apparatus.

FIG. 7 is a flowchart for describing a data communication flow in communication method M2.

DESCRIPTION OF EMBODIMENTS

A communication control method in an interchangeable lens serving as an accessory device and a camera main body serving as an imaging apparatus according to the present invention will be described in detail with reference to the attached drawings. First, definition of terms in the present embodiment will be described.

“Communication format” indicates rules regarding the entire communication between the camera main body and the interchangeable lens. “Communication method” means the clock-synchronized method and asynchronous method, with the clock-synchronized method being communication method A and the asynchronous method being communication method B. “Data format” indicates whether or not a communication standby request signal (BUSY signal) is added, with a data format where adding a BUSY signal is permitted is “format F1”, while a data format where adding a BUSY signal is forbidden is “format F2”.

“Communication mode” means a combination of communication method and data format, and the following three communication modes will be described in the present embodiment. “Communication mode M1” is a communication mode of communication method A and format F1, and “communication mode M2” is a communication mode of communication method B and format F1. “Communication mode M3” is a communication mode of communication method B and format F2.

The present invention relates to communication control between the camera main body and interchangeable lens in the communication mode M2. An imaging system having a camera main body and interchangeable lens capable of communicating by switching between multiple communication modes including the communication mode M2 is illustrated in the following embodiment. Appropriately switching the communication mode and performing communication in this way enables an appropriate communication mode to be selected in accordance with the combination of camera main body and interchangeable lens, and the shooting mode.

For example, in a case where the camera main body and interchangeable lens are compatible with the communication mode M3, and are to exchange great amounts of data, the communication mode of each is switched to the communication mode M3, and thereafter high-speed data communication is executed where attaching BUSY signals is forbidden. In a case where data processing requires a certain amount of time at the interchangeable lens, the communication mode of each of the camera main body and interchangeable lens is switched to the communication mode M2, and thereafter data communication is executed where attaching BUSY signals is permitted. Thus, data communication can be executed between the camera main body and interchangeable lens that does not lead to breakdown of communication.

FIG. 1 illustrates the configuration of an imaging system (hereinafter referred to as camera system) including a camera main body 200 serving as an imaging apparatus that is the first embodiment of the present invention, and an interchangeable lens 100 serving as an accessory device detachably mounted thereto.

The camera main body 200 and interchangeable lens 100 perform transmission of control commands and internal information via communication units that each has. Each communication unit supports multiple communication formats, and is capable of selecting an optimal communication format under various situations by synchronously switching to the same communication format as each other in accordance with the type of communication data and purpose of communication.

First, a specific configuration of the interchangeable lens 100 and camera main body 200 will be described. The interchangeable lens 100 and camera main body 200 are mechanically and electrically connected via a mount 300 that is a coupling mechanism. The interchangeable lens 100 receives supply of power from the camera main body 200 via power source terminal, omitted from illustration, provided to the mount 300, and controls later-described actuators of various types, and a lens microprocessor 111. The interchangeable lens 100 and camera main body 200 communicate with each other via communication terminals (illustrated in FIG. 2) provided to the mount 300.

The interchangeable lens 100 has an imaging optical system. The imaging optical system includes, in order from an object OBJ side, a field lens 101, a zoom lens 102 that changes zoom power, a diaphragm unit 114 that adjusts the quantity of light, an image stabilization lens 103, and a focus lens 104 that performs focal point adjustment.

The zoom lens 102 and focus lens 104 are respectively held by lens holding frames 105 and 106. The lens holding frames 105 and 106 are movably guided in the optical axis direction, illustrated in the diagram as a dotted line, by a guide shaft omitted from illustration, and are driven in the optical axis direction by respective stepping motors 107 and 108. The stepping motors 107 and 108 move the zoom lens 102 and focus lens 104 synchronously with driving pulses.

The image stabilization lens 103 reduces image blurring due to shaking of hands and so forth, by moving in a direction orthogonal to the optical axis of the imaging optical system.

The lens microprocessor 111 is an accessory control unit for controlling operations of the parts within the interchangeable lens 100. The lens microprocessor 111 receives control commands transmitted from the camera main body 200, and receives transmission requests for lens data, via a lens communication unit 112 serving as an accessory communication unit. The lens microprocessor 111 performs lens control corresponding to the control commands, and transmits lens data corresponding to transmission requests to the camera main body 200 via the lens communication unit 112.

The lens microprocessor 111 also outputs driving signals to a zoom drive circuit 119 and focus drive circuit 120, in response to commands relating to zooming and focusing, out of the control commands, thereby driving the stepping motors 107 and 108. Accordingly, zoom processing where zooming operations by the zoom lens 102 are controlled, and autofocus processing where focal point adjustment operations by the focus lens 104 are controlled, are carried out.

The diaphragm unit 114 is configured including diaphragm blades 114 a and 114 b. The state of the diaphragm blades 114 a and 114 b is detected by a Hall effect device 115, and input to the lens microprocessor 111 via an amplifying circuit 122 and an A/D conversion circuit 123. The lens microprocessor 111 outputs drive signals to a diaphragm drive diaphragm circuit 121 based on input signals from the A/D conversion circuit 123, and drives a diaphragm actuator 113. Accordingly, light quantity adjustment operations by the diaphragm unit 114 are controlled.

Further, the lens microprocessor 111 drives an anti-vibration actuator 126 via an anti-vibration drive circuit 125 in accordance with shaking detected by an unshown shaking sensor such as a vibration gyro or the like provided within the interchangeable lens 100. Accordingly, anti-vibration processing that controls shifting operations of the image stabilization lens 103 is performed.

The camera main body 200 has an imaging device 201 such as a CCD sensor or CMOS sensor or the like, an A/D conversion circuit 202, a signal processing circuit 203, a recording unit 204, a camera microprocessor 205, and a display unit 206.

The imaging device 201 performs photoelectric conversion of a subject image formed by the imaging optical system within the interchangeable lens 100, and outputs electric signals (analog signals). The A/D conversion circuit 202 coverts analog signals from the imaging device 201 into digital signals. The signal processing circuit 203 subjects digital signals from the A/D conversion circuit 202 to various types of image processing, and generates video signals.

The signal processing circuit 203 also generates luminance information indicating the contrast state of the subject image from the video signals, i.e., focus information indicating the focal state of the imaging optical system and the exposure state. The signal processing circuit 203 outputs the video signals to the display unit 206, and the display unit 206 displays the video signals as a live preview image used for confirming the composition, focus state, and so forth, of the video signals.

The camera microprocessor 205 serving as a camera control unit performs control of the camera main body 200 in accordance with input from camera operating members, such as an imaging instructing switch, various types of setting switches, and so forth, that are omitted from illustration. The camera microprocessor 205 also transmits control commands relating to zooming operations of the zoom lens 102 in accordance with operation of an unshown zoom switch to the lens microprocessor 111, via a camera data transmission/reception unit 208. The camera microprocessor 205 further transmits control commands relating to light quantity adjustment operations of the diaphragm unit 114 in accordance with luminance information, and focal point adjustment operations of the focus lens 104 in accordance with focus information, to the lens microprocessor 111 via the camera data transmission/reception unit 208 b.

Next, communication circuits configured between the camera main body 200 and interchangeable lens 100, and communication control performed therebetween, will be described with reference to FIG. 2. The camera microprocessor 205 has a function of managing communication formats between itself and the lens microprocessor 111, and a function of notifying the lens microprocessor 111 of transmission requests and so forth. The lens microprocessor 111 also has a function of generating lens data and a function of transmitting the lens data.

The camera microprocessor 205 and lens microprocessor 111 perform communication through communication terminals provided to the mount 300, and communication interface circuits 208 a and 112 a provided to each respectively. Here, the communication interface circuit 208 a and camera data transmission/reception unit 208 b will be collectively referred to as a camera communication unit 208, and the communication interface circuit 112 a and a lens data transmission/reception unit 112 b will be collectively referred to as the lens communication unit 112.

In the present embodiment, the camera microprocessor 205 and the lens microprocessor 111 perform serial communication by three-line communication method A and communication method B using three channels.

One of the above-described three channels is the clock channel in the communication method A, and is a notification channel serving as a transmission request channel in the communication method B. One of the remaining two channels is a first data communication channel (accessory data communication channel) that is used for lens data transmission from the lens microprocessor 111 to the camera microprocessor 205. The other one channel is a second data communication channel (imaging apparatus data communication channel) used for transmission of camera data from the camera microprocessor 205 to the lens microprocessor 111.

Lens data transmitted from the lens microprocessor 111 to the camera microprocessor 205 as signals over the first data communication channel will be referred to as lens data signals DLC. Camera data transmitted from the camera microprocessor 205 to the lens microprocessor 111 as signals over the second data communication channel will be referred to as camera data signals DCL.

First, communication by the communication method A will be described. In the communication method A, clock signals LCLK are output from the camera microprocessor 205 serving as the communication master to the lens microprocessor 111 serving as a communication slave, via the clock channel. The camera data signals DCL include control commands, transmission request commands, and so forth, from the camera microprocessor 205 to the lens microprocessor 111. On the other hand, the lens data signals DLC include various types of data transmitted from the lens microprocessor 111 to the camera microprocessor 205 synchronously with the clock signals LCLK. The camera microprocessor 205 and the lens microprocessor 111 are capable of communicating by the full-duplex communication system where transmission and reception is performed mutually and simultaneously in synchronization with common clock signals LCLK.

FIGS. 3A through 3C illustrate waveforms of signals exchanged between the camera microprocessor 205 and lens microprocessor 111. Rules decided for procedures for this exchange are referred to as a communication protocol.

FIG. 3A illustrates signal waveforms of one frame, that is the smallest increment of communication. First, the camera microprocessor 205 outputs clock signals LCLK of which clock pulses of eight cycles is one set, and transmits camera data signals DCL to the lens microprocessor 111 synchronously with the clock signals LCLK. At the same time, the camera microprocessor 205 receives the lens data signals DLC output from the lens microprocessor 111 synchronously with the clock signals LCLK.

Thus, one byte (eight bits) of data is transmitted and received between the lens microprocessor 111 and camera microprocessor 205 synchronously with the ones set of clock signals LCLK. The period for transmission/reception of one byte of data is called a data frame. After transmission/reception of this one byte of data, the lens microprocessor 111 transmits a signal notifying a communication standby request BUSY to the camera microprocessor 205 (hereinafter referred to as a BUSY signal), whereby a communication standby period is inserted. This communication standby period is referred to as a BUSY frame, and the camera microprocessor 205 is in a communication standby state while receiving the BUSY frame. A communication increment of one set of data frame period and BUSY fame period makes of one frame. Depending on the communication state, there are cases where no BUSY frame is added, in which cases one frame is made up of just the data frame period.

FIG. 3B illustrates the signal waveforms when the camera microprocessor 205 transmits a request command CMD1 to the lens microprocessor 111, and receives corresponding two-byte lens data DT1 (DT1 a, DT1 b) from the lens microprocessor 111. FIG. 3B illustrates an example of data communication being executed in accordance with “communication CMD1”.

Types of lens data DT and byte counts corresponding to each of multiple types of commands CMD are stipulated beforehand regarding the camera microprocessor 205 and lens microprocessor 111. When the camera microprocessor 205 that is the communication master transmits a particular command CMD to the lens microprocessor 111, the lens microprocessor 111 transmits a clock count that is necessary based on the lens data byte count corresponding to this command CMD to the camera microprocessor 205. The processing of the lens microprocessor 111 in accordance with the command CMD1 includes superimposing a BUSY signal on the clock signals LCLK in each frame, with the above-described BUSY frame being inserted between the data frames.

In communication CMD1, the camera microprocessor 205 transmits clock signals LCLK to the lens microprocessor 111, and further transmits a request command CMD1 requesting transmission of lens data DT1 to the lens microprocessor 111 as camera data signals DCL. The lens data signals DLC in this frame is handled as invalid data.

Next, after having output eight cycles of clock signals LCLK over the clock channel, the camera microprocessor 205 switches the clock channel at the camera microprocessor side (camera main body side) from output settings to input settings. Upon the switching of the clock channel at the camera microprocessor side being completed, the lens microprocessor 111 switches the clock channel at the lens microprocessor 111 side (interchangeable lens side) from input settings to output settings. The lens microprocessor 111 then sets the voltage level of the clock channel to Low, to notify the camera microprocessor 205 of a communication standby request BUSY. Accordingly, a BUSY signal is superimposed on the clock channel. During the period in which the communication standby request BUSY is being notified, the camera microprocessor 205 maintains input settings of the clock channel, and stops communication to the lens microprocessor 111.

The lens microprocessor 111 generates lens data DT1 corresponding to the transmission request command CMD1 during notification of the communication standby request BUSY. Upon preparation for transmitting the lens data DT1 as the lens data signals DLC of the next frame, the signal level of the clock channel at the lens microprocessor side is switched to High, and the communication standby request BUSY is cancelled.

Upon recognizing the cancellation of the communication standby request BUSY, the camera microprocessor 205 transmits one frame of clock signals LCLK to the lens microprocessor 111, thereby receiving lens data DT1 a from the lens microprocessor 111. The camera microprocessor 205 that has output eight cycles of clock signals LCLK again in the next frame, and the lens microprocessor 111 repeats the same operations as described above, whereby the camera microprocessor 205 receives lens data DT1 b from the lens microprocessor 111.

FIG. 3C illustrates signal waveforms when the camera microprocessor 205 transmits a request command CMD2 to the lens microprocessor 111 and receives three bytes of lens data DT2 (DT2 a through DT2 c) corresponding thereto from the lens microprocessor 111. FIG. 3C illustrates an example of data communication being executed in accordance with communication CMD2. The processing of the lens microprocessor 111 in accordance with the request command CMD2 in this communication CMD2 includes superimposing a BUSY signal on the clock channel only in the first frame. That is to say, the lens microprocessor 111 does not superimpose a BUSY signal on the subsequent second frame through fourth frame.

Accordingly, no BUSY frame is inserted between frames from the second frame through the fourth frame, and the standby period between frames can be reduced. However, the lens microprocessor 111 cannot transmit a communication standby request to the camera microprocessor 205 during periods where BUSY frames are not inserted. Accordingly, the data count for transmission, transmission intervals, the order of priority of communication processing within the lens microprocessor 111, and so forth, need to be decided beforehand, so that there is no breakdown of communication as a result.

Next, the communication method B will be described. The communication mode M2 where communication is performed by format F1 using the communication method B will be described as well. FIG. 4 illustrates waveforms of communication signals exchanged between the camera microprocessor 205 and the lens microprocessor 111 in the communication mode M2. A BUSY frame is selectively added to the lens data signals DLC in the format F1, as described earlier.

The transmission request channel is used for notification of lens data transmission requests and so forth, from the camera microprocessor 205 serving as the communication master to the lens microprocessor 111 serving as a communication slave, in the communication method B. Notification over the transmission request channel is performed by switching the level (voltage level) of signals on this transmission request channel between High (first level) and Low (second level). In the following description, signals supplied to the transmission request channel in the communication method B will be referred to as transmission request signals RTS.

The first data communication channel is used for transmission of lens data signals DLC including various types of data from the lens microprocessor 111 to the camera microprocessor 205, in the same way as with the communication method A. The second data communication channel is also used for transmission of camera data signals DCL including control commands and transmission request commands and so forth from the camera microprocessor 205 to the lens microprocessor 111, in the same way as in communication method A.

Unlike the communication method A, the camera microprocessor 205 and lens microprocessor 111 have the communication speed set beforehand and transmit/receive at a communication bitrate based on this setting in the communication method B, instated of performing data transmission/reception synchronously with common clock signals. The communication bitrate indicates the amount of data that can be transmitted per second, and the unit is expressed as bps (bits per second).

Note that in the present embodiment, the camera microprocessor 205 and lens microprocessor 111 communicate by the full-duplex communication system where mutual transmission/reception is performed in this communication method B, in the same way as with the communication method A.

FIG. 4 illustrates signal waveforms of one frame, that is the smallest increment of communication. The breakdown of the data format of one frame partially differs between the camera data signals DCL and lens data signals DLC.

First, the data format of the lens data signals DLC will be described. One frame of lens data signals DLC is made up of the data frame at the first half and the subsequent BUSY frame. The signal level of the lens data signals DLC is maintained at High in a state where data transmission is not being performed.

The lens microprocessor 111 sets the voltage level of the lens data signals DLC to LOW for a period of one bit, in order to notify the camera microprocessor 205 of the start of transmission of one frame of the lens data signals DLC. This one-bit period is called a start bit ST, and the data frame is started from the start bit ST. The lens microprocessor 111 subsequently transmits one byte of lens data in an eight-byte period from the second bit following the start bit ST through the ninth bit.

The array of data bits is an MSB (Most Significant Bit)-first format, starting from the highest order data D7, continuing in order to data D6, data D5, and ends on the lowest order data D0. The lens microprocessor 111 then adds one bit of parity information (PA) at the tenth bit, and sets the voltage level of the lens data signals DLC to HIGH for the period of a stop bit SP indicating the last of one frame. Thus, the data frame period started from the start bit ST is ended. Note that the parity information does not have to be one bit, and that parity information of multiple bits may be added. The parity information is not indispensable either, and a format may be used where parity information is not added.

Next, the lens microprocessor 111 adds a BUSY frame after the stop bit SP, as indicated by “DLC (WITH BUSY)” in the drawing. The BUSY frame indicates the period of communication standby request BUSY where the lens microprocessor 111 notifies the camera microprocessor 205, in the same way as in the communication method A. The lens microprocessor 111 maintains the signal level of the lens data signals DLC to Low, until the communication standby request BUSY is cancelled.

On the other hand, there are cases where notification of communication standby request BUSY from the lens microprocessor 111 to the camera microprocessor 205 is unnecessary. Accordingly, a data format where one frame is configured without adding a BUSY frame (hereinafter also referred to as BUSY notification) is also provided for such cases, as indicated by “DLC (WITHOUT BUSY)” in the drawing. That is to say, selection can be made regarding the data format of the lens data signals DLC between one with a BUSY notification added and one not added, in accordance with the processing situation at the lens microprocessor side.

Description will be made regarding the method of the camera microprocessor 205 identifying between whether or not there is a BUSY notification. The signal waveform indicated in “DLC (WITHOUT BUSY)” in FIG. 4 and the signal waveform indicated in “DLC (WITH BUSY)” in FIG. 4 include bit positions B1 and B2. The camera microprocessor 205 selects one of the bit positions B1 and B2 as a BUSY identification position P for identifying whether or not there is a BUSY notification. In this way, the present embodiment employs a data format where the BUSY identification position P is selected from bit positions B1 and B2. Thus, the problem of different processing times from transmission of the lens data signals DLC data frame until the BUSY notification (DLC is Low) is finalized, depending on the processing capabilities of the lens microprocessor 111, can be handled.

Whether the bit position B1 or the bit position B2 is to be the BUSY identification position P is decided by communication between the camera microprocessor 205 and lens microprocessor 111 before performing communication by communication method B. Note that the BUSY identification position P does not need to be fixed to one bit position of B1 and B2, and may be changed in accordance with the processing capabilities of the camera microprocessor 205 and lens microprocessor 111. Also note that the BUSY identification position P is not restricted to B1 or B2, and may be set at a predetermined location after the stop bit SP.

Now, the reason why the BUSY frame added to the clock signals LCLK in communication method A is added to the lens data signals DLC in communication method B as a data format will be described.

In the communication method A, the clock signals LCLK output by the camera microprocessor 205 that is the communication master and the BUSY signal output by the lens microprocessor 111 that is a communication slave need to be exchanged over the same clock channel. Accordingly, collision of the outputs of the camera microprocessor 205 and lens microprocessor 111 is prevented by time division. That is to say, collision of the outputs can be prevented by appropriately assigning outputtable periods for the camera microprocessor 205 and lens microprocessor 111 in the clock channel.

However, in this time division method, collision of the outputs of the camera microprocessor 205 and lens microprocessor 111 needs to be prevented in a sure manner. To this end, a certain output-forbidden period where output of the microprocessors 205 and 111 is forbidden is inserted between the point in time at which the camera microprocessor 205 has completed output of the eight pulses of clock signals LCLK and the point in time at which output of a BUSY signal by the lens microprocessor 111 is permitted. This output-forbidden period is a communication invalid period where the camera microprocessor 205 and lens microprocessor 111 cannot communicate, and thus leads to deterioration of effective communication speed.

In order to solve this problem, the communication method B employs the data format where the BUSY frame from the lens microprocessor 111 is added to the lens data signals DLC on the first data communication channel, which is a dedicated output channel for the lens microprocessor 111.

Next, the data format of the camera data signals DCL will be described. The specification of one data frame is the same as with the lens data signals DLC. However, adding of the BUSY frame to the camera data signals DCL is forbidden, unlike the lens data signals DLC.

Next, the procedures of communication by the communication method B between the camera microprocessor 205 and lens microprocessor 111 will be described. First, when an event occurs to start communication with the lens microprocessor 111, the camera microprocessor 205 sets the voltage level of the transmission request signals RTS to Low (hereinafter, this will be referred to as asserting a transmission request signal RTS), thereby notifying a communication request to the lens microprocessor 111.

Upon detecting the communication request by the voltage level of transmission request signals RTS having changed to Low, the lens microprocessor 111 preforms generating processing of lens data signals DLC to transmit to the camera microprocessor 205. Once transmission preparation of the lens data signals DLC has been made, transmission of one frame of lens data signals DLC is started via the first data communication channel. Now, the lens microprocessor 111 starts transmission of the lens data signals DLC within the set time that has been mutually set between the camera microprocessor 205 and the lens microprocessor 111, from the point in time that the voltage level of the transmission request signals RTS has gone to Low.

That is to say, it is sufficient in the communication method B for the lens data to be transmitted to be finalized between the point in time that the voltage level of the transmission request signals RTS goes to Low up to transmission of the lens data signals DLC being started. There are no strict restrictions as with the communication method A, where the lens data to be transmitted has to be finalized by the point in time at which the first clock pulse is input, so the timing at which to start transmitting the lens data signals DLC can be given more freedom.

Next, the camera microprocessor 205 returns the voltage level of the transmission request signals RTS to High, in accordance with detection of the start bit ST added to the head of the lens data signals DLC data frame received from the lens microprocessor 111. Hereafter, this will be referred to as negating the transmission request signal RTS. Accordingly, the transmission request is cancelled, and transmission of the camera data signals DCL over the second communication channel is started. Note that either of negating transmission request signals RTS and starting transmission of camera data signals DCL may be first, and that it is sufficient for this to be performed by the time that reception of the lens data signals DLC data frame is completed.

In a case where the lens microprocessor 111 that has transmitted the lens data signals DLC data frame needs to notify the camera microprocessor 205 of a communication standby request BUSY, a BUSY frame is added to the lens data signals DLC. The camera microprocessor 205 monitors whether or not there are communication standby request BUSY notifications, and asserting transmission request signals RTS is forbidden while a communication standby request BUSY is being notified, for the next transmission request.

The lens microprocessor 111 executes necessary processing during the period where communication from the camera microprocessor 205 has been put on standby by the communication standby request BUSY, and the communication standby request BUSY is cancelled after preparation for the next communication is ready. The camera microprocessor 205 is permitted to assert transmission request signals RTS for the next transmission request, under the conditions that the communication standby request BUSY has been cancelled and that transmission of the camera data signals DCL data frame has been completed.

Thus, according to the present embodiment, the lens microprocessor 111 starts transmission of a lens data signals DLC data frame to the camera microprocessor 205 in accordance with transmission request signals RTS having been asserted with a communication start event at the camera microprocessor 205 as a trigger. The camera microprocessor 205 then starts transmission of a camera data signals DCL data frame to the lens microprocessor 111 in accordance with having detected the start bit ST of the lens data signals DLC.

The lens microprocessor 111 adds a BUSY frame after the lens data signals DLC data frame for a communication standby request BUSY as necessary, and hereafter cancels the communication standby request BUSY, thereby completing communication processing of one frame. According to this communication processing, one byte of communication data is mutually exchanged between the camera microprocessor 205 and lens microprocessor 111.

Next, the communication mode M3 where communication is performed by the format F2 using the communication method B will be described. FIG. 5A illustrates waveforms of the communication signals exchanged between the camera microprocessor 205 and lens microprocessor 111 in the communication mode M3. In FIG. 5A, the waveforms for communication signals in a case of consecutively transmitting three frames of data are illustrated. Adding a communication standby request BUSY to lens data signals DLC is forbidden in format F2, as described earlier.

In the lens data signals DLC data format in the communication mode M3, one frame is made up of a data frame alone, and here is no BUSY frame. Accordingly, the lens microprocessor 111 cannot notify the camera microprocessor 205 of a communication standby request BUSY in the communication mode M3.

This format F2 is used for usages of performing continuous communication with reduced inter-frame intervals, when transferring relatively large amounts of data between the camera microprocessor 205 and lens microprocessor 111. That is to say, the format F2 enables large amounts of data to be communicated at high speeds.

Next, the communication control processing between the camera microprocessor 205 and lens microprocessor 111 that is a feature of the present embodiment will be described. FIG. 5B illustrates waveforms of communication signals when each of the camera microprocessor 205 and lens microprocessor 111 consecutively transmit and receive n frames of camera data signals DCL and lens data signals DLC. The camera microprocessor 205 asserts transmission request signals RTS when an event of starting communication with the lens microprocessor 111 occurs. In the format F2, the camera microprocessor 205 does not need to negate the transmission request signals RTS in each frame, unlike with the format F1. Accordingly, the state of asserting transmission request signals RTS is maintained as long as a state where data can be consecutively transmitted/received.

Upon detecting a communication request by asserting of transmission request signals RTS, the lens microprocessor 111 performs processing to generate lens data signals DLC to transmit to the camera microprocessor 205. Once preparation for transmission of the lens data signals DLC is ready, transmission of the first frame of lens data signals DLC (DL1) is started over the first data communication channel.

The lens microprocessor 111 that has transmitted the first frame of the lens data signals DLC data frame confirms the transmission request signals RTS again. In a case where the transmission request signals RTS are in an asserted state, the lens microprocessor 111 transmits the second frame of lens data signals DLC (DL2) to the camera microprocessor 205 in succession after the first frame of which transmission has been completed. Thus, the lens data signals DLC (DL1 through DLn) are successively transmitted to the camera microprocessor 205 from the lens microprocessor 111 as long as the asserted state of transmission request signals RTS is maintained. Once transmission of the predetermined number of frames n has been completed, transmission of lens data signals DLC is stopped.

In response to detection of the start bit ST for each frame of lens data signals DLC from the lens microprocessor 111 being detected, the camera microprocessor 205 starts transmission of n frames of camera data signals DCL (DC1 through DCn) over the second communication channel.

FIG. 5C illustrates waveforms of communication signals in a case where a temporary communication standby has been instructed from the camera microprocessor 205 or lens microprocessor 111 during the communication of consecutive data exchange illustrated in FIG. 5B. In this case as well, the lens microprocessor 111 starts transmission of lens data signals DLC due to transmission request signals RTS being asserted by the camera microprocessor 205, and the camera microprocessor 205 starts transmission of camera data signals DCL in accordance with detection of a start bit ST thereof.

T2 w 1 indicates a communication standby period that is a period regarding which communication standby has been instructed from the camera microprocessor 205, this instruction being notified to the lens microprocessor 111 by temporary negation of transmission request signals RTS. Upon detecting that the transmission request signals RTS have been negated, the lens microprocessor 111 pauses transmission after having completed transmission of the frame of lens data signals DLC that is being transmitted at the time of detection (DL6 in the drawing: hereinafter referred to as a pause frame).

In response to the pausing of transmission of lens data signals DLC, the camera microprocessor 205 also pauses transmission of the camera data signals DCL after having transmitted the frame corresponding to the above pause frame (DC6), out of the camera data signals DCL. According to this communication control, management can be performed so that the number of transmitted frames of lens data signals DLC and camera data signals DCL can be made to be the same even if a communication standby instruction occurs during communication of consecutive data exchange.

Once the communication standby request event is gone, the camera microprocessor 205 can instruct resuming of communication to the lens microprocessor 111, by asserting the transmission request signals RTS again. Transmission of lens data signals DLC by the lens microprocessor 111 is resumed from the next frame (DL7: hereinafter referred to as resume frame) after the pause frame, in accordance with the communication resume instruction. Upon detecting the start bit ST of the resume frame, the camera microprocessor 205 resumes transmission of camera data signals DCL from the frame (DC7) corresponding to the resume frame above.

On the other hand, T2 w 2 represents a communication standby period which is a period that communication standby has been instructed by the lens microprocessor 111. After ending of the communication standby period T2 w 1 in the drawings, neither the camera microprocessor 205 nor the lens microprocessor 111 has instructed communication standby, and the above-described resume frames DL7 and DC7, and subsequent frames DL8, DC8 through DL9, and DC9, are subjected to consecutive data transmission/reception, in that order.

When transmission of frame DL9 within the lens microprocessor 111 (reception of the frame DC9 at the camera microprocessor 205) is completed, a communication standby request event occurs, whereby the lens microprocessor 111 notifies the camera microprocessor 205 of a communication standby instruction. When the transmission request signals RTS are in an asserted state, the lens microprocessor 111 does not transmit lens data signals DLC, thereby notifying the camera microprocessor 205 from the lens microprocessor 111 that communication will be paused.

The camera microprocessor 205 constantly monitors the start bit ST of each frame in the lens data signals DLC, and is stipulated such that, in a case where the start bit ST is not detected, transmission of the next frame of camera data signals DCL is stopped. In a case where the camera microprocessor 205 does not receive lens data signals DLC from the lens microprocessor 111 (DL10 in the drawing) even though it is asserting transmission request signals RTS, communication is paused without transmitting the camera data signals DCL (DC10). Note that the camera microprocessor 205 maintains the transmission request signals RTS in an asserted state during the communication standby period T2 w 2 under instruction from the lens microprocessor 111.

Thereafter, the communication standby request event in the lens microprocessor 111 is gone, and the lens microprocessor 111 resumes transmission of the resume frame DL10 of the lens data signals DLC. The camera microprocessor 205 resumes transmission of the corresponding frame DC10 in the camera data signals DCL in accordance with having detected the start bit ST of this resume frame DL10.

Next, the procedures of deciding the communication format performed between the camera microprocessor 205 and the lens microprocessor 111 will be described with reference to FIG. 6. The camera microprocessor 205 and lens microprocessor 111 perform the communication control of the flowcharts in FIGS. 6 and 7, following a communication control program that is a computer program. Note that “S” in FIGS. 6 and 7 means step.

First, when the interchangeable lens 100 is mounted to the camera main body 200, in step S100 and step S200 the camera microprocessor 205 and lens microprocessor 111 set the communication format to an initial communication format, regarding which establishing communication is guaranteed. The initial communication format here may be a combination of communication method and data format disclosed in the present embodiment, or may be another communication format. In a case where an asynchronous communication format is selected as the initial communication format, a BUSY identification position P is preferably set, so that communication can be executed between any combination of camera and interchangeable lens.

Next, in step S101, the camera microprocessor 205 transmits camera identification information, representing communication formats that the camera main body 200 is capable of handling, to the lens microprocessor 111. Also, in step S202, the lens microprocessor 111 transmits lens identification information, representing communication formats that the interchangeable lens 100 is capable of handling, to the camera microprocessor 205.

The “identification information” here includes information indicating which of the clock-synchronized method and the asynchronous method there is compatibility with, and information indicating the range of communication bitrates that can be handled. Information indicating the BUSY identification position P is also included in the identification information.

The camera microprocessor 205 receives the lens identification information in step S102. The lens microprocessor 111 receives the camera identification information in step S201. Although the lens identification information is transmitted after the camera identification information is transmitted in the flowchart in FIG. 6, the transmission of the camera identification information and the transmission of the lens identification information may be at the same time. Further, the camera identification information may be transmitted after the lens identification information is transmitted.

Next, in step S103 and step S203, the communication format to be used in subsequent communication is set. Specifically, the camera microprocessor 205 and lens microprocessor 111 decide, out of the communication bitrates that each other can handle, the fastest rate as the communication bitrate. Also, a position out of BUSY identification positions that each other is capable of handling, that is closest to the stop bit SP, is set as the BUSY identification position.

Next, a data communication flow in the asynchronous communication method will be described with reference to FIG. 7. FIG. 7 describes a communication flow in a data format where adding a BUSY signal is permitted.

The camera microprocessor 205 monitors whether or not a communication event for starting communication with the lens microprocessor 111 has occurred, and in a case where a communication event has occurred in step S110, advances to step S111. Transmission request signals RTS are asserted in step S111 as described so far, thereby placing a communication request with the lens microprocessor 111.

The lens microprocessor 111 monitors whether or not there has been assertion of transmission request signals RTS, and upon recognizing that there has been assertion of transmission request signals RTS in step S210, advances to step S211. In step S211, the lens microprocessor 111 transmits lens data signals DLC to the camera microprocessor 205 via the first data communication channel.

Upon receiving lens data signals DLC from the lens microprocessor 111 (YES in step S112), the camera microprocessor 205 advances to step S113, and negates transmission request signals RTS. The flow then advances to step S114, and camera data signals DCL are transmitted to the lens microprocessor 111 via the second data communication channel.

Upon detecting start of reception of camera data signals DCL in step S212, the lens microprocessor 111 advances to step S213, and performs reception processing of the camera data signals DCL. In parallel with the processing of step S213, determination is made in step S214 regarding whether or not there is need to notify the camera microprocessor 205 of a communication standby request BUSY. In a case where there is no need to make notification of a communication standby request BUSY, the flow advances to step S218, and stands by until reception of the camera data signals DCL ends.

On the other hand, in a case where there is a need for the lens microprocessor 111 to notify the camera microprocessor 205 of a communication standby request BUSY, the flow advances to step S215, and a BUSY frame is added to the lens data signals DLC. The lens microprocessor 111 executes necessary processing while notification of the communication standby request BUSY is being notified, and after preparation for the next communication has been completed (Yes in step S216), the communication standby request BUSY is cancelled (step S217). After having canceled the communication standby request BUSY, the flow advances to step S218, and stands by until reception of the camera data signals DCL is completed. Upon reception of the camera data signals DCL is complete (Yes in step S218), the flow returns to step S210, and monitoring of whether transmission request signals RTS have been asserted is continued.

Upon having received the communication standby request BUSY in step S115, the camera microprocessor 205 stands by until the communication standby request BUSY is cancelled. When the communication standby request BUSY is cancelled (YES in step S116), the flow advances to step S117, and determination is made regarding whether or not transmission of the camera data signals DCL has been completed. Even in a case where notification of a communication standby request BUSY has not been received in step S115, the flow advances to step S117, and determination is made regarding whether or not transmission of the camera data signals DCL has been completed. If determination is made in step S117 that transmission of the camera data signals DCL has been completed, the flow returns to step S110, and monitoring of whether or not a communication event has occurred is continued.

As described above, the present embodiment relates to communication control in asynchronous (communication method B) communication made up of three channels. A communication standby request BUSY is transmitted from the lens microprocessor 111 to the camera microprocessor 205, via the first data communication channel that is a dedicated output channel of the lens microprocessor 111. On the other hand, a transmission request signals RTS from the camera microprocessor 205 is transmitted from the camera microprocessor 205 to the lens microprocessor 111 via the notification channel serving as a dedicated output channel of the camera microprocessor 205.

Thus, the communication standby request BUSY from the lens microprocessor 111 is exchanged via the dedicated output channel of the lens microprocessor 111, and the transmission request signal RTS from the camera microprocessor 205 is exchanged via the dedicated output channel of the camera microprocessor 205. Accordingly, the communication-invalid period between the camera microprocessor 205 and lens microprocessor 111 can be shortened, and as a result, effective communication speed can be increased.

With regard to the start timing of communication, data transmission from the lens microprocessor 111 to the camera microprocessor 205 is started first. The camera microprocessor 205 starts data transmission in accordance with having detected a start bit ST of a data frame transmitted from the lens microprocessor 111. Setting the start timing for communication in this way enables the lens microprocessor 111, which has received the transmission request signal RTS, to have freedom in the timing for starting data transmission to the camera microprocessor 205.

For example, the start timing for data transmission can be changed in accordance with the information processing capabilities of the lens microprocessor 111. Accordingly, the communication speed between the camera main body 200 and the interchangeable lens 100 can be improved without leading to breakdown of communication.

The above-described embodiment is only a representative example, and various modifications and alterations may be made to the embodiments when carrying out the present invention. For example, although an example of using an interchangeable lens as the accessory device has been illustrated in the above embodiment, a strobe or the like may be used as long as having function of communicating with the imaging apparatus.

The present invention can also be realized by processing of a program realizing one or more of functions of the above-described embodiment being supplied to a system or apparatus via a network or recording medium, and one processor or more in the system or apparatus in the computer reading out and executing the program. This can also be realized by a circuit having one or more function (e.g., an ASIC).

According to the present invention, an accessory device and imaging apparatus capable of performing high-speed data exchange without leading to breakdown of communication, without adding new channels, can be obtained.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 

The invention claimed is:
 1. An accessory device detachably mountable to an imaging apparatus, the accessory device comprising: an accessory communication circuitry that provides, between itself and the imaging apparatus, a notification channel used for notification from the imaging apparatus to the accessory device, an accessory data communication channel used for data transmission from the accessory device to the imaging apparatus, and an imaging apparatus data communication channel used for data transmission from the imaging apparatus to the accessory device; and an accessory control circuitry configured to control the accessory communication circuitry, wherein the accessory control circuitry transmits a first data to the imaging apparatus via the accessory data communication channel, in response to receiving, via the notification channel, a transmission request signal, the transmission request signal being a signal for requesting transmission of data from the accessory device to the imaging apparatus, and receives, via the imaging apparatus data communication channel, a second data transmitted, to the accessory device, from the imaging apparatus in response to the imaging apparatus starting to receive the first data.
 2. The accessory device according to claim 1, wherein a period to transmit the first data and a period to receive the second data are partially overlapped.
 3. The accessory device according to claim 1, wherein the transmission request signal is expressed by changing a voltage level of the notification channel.
 4. The accessory device according to claim 3, wherein the accessory control circuitry transmits the first data within a predetermined period after the voltage level of the notification channel changes.
 5. The accessory device according to claim 3, wherein the transmission request signal is expressed by changing the voltage level of the notification channel from a first level to a second level which is different from the first level, and the accessory control circuitry transmits a third data to the imaging apparatus, via the accessory data communication channel, in a case where the voltage of the notification channel is the second level after transmitting the first data.
 6. The accessory device according to claim 1, wherein the accessory device performs communication with the imaging apparatus by switching between a data format where data frames are transmitted without a communication standby period, and a data format where data frames are transmitted with a communication standby period.
 7. The accessory device according to claim 6, wherein in a case where the communication format, between itself and the imaging apparatus, is the data format where data frames are transmitted with the communication standby period, a number of data which the accessory control circuitry transmitted to the imaging apparatus before the communication standby period and a number of data which the accessory control circuitry received from the imaging apparatus before the communication standby period are the same number.
 8. The accessory device according to claim 6, wherein the transmission request signal is expressed by changing the voltage level of the notification channel from a first level to a second level which is different from the first level, and the communication standby period is expressed by the voltage level of the notification channel in the first level.
 9. The accessory device according to claim 6, wherein the accessory control circuitry pauses data transmission to the imaging apparatus while the communication standby request event occurring in the accessory device.
 10. The accessory device according to claim 1, wherein the accessory device performs an asynchronous communication with the imaging apparatus.
 11. The accessory device according to claim 1, wherein the accessory device is communicable with the imaging device by switching communication methods between a clock-synchronized communication method synchronized with clock signals and an asynchronous communication method, and the accessory control circuitry receives, via the notification channel, the clock signals transmitted from the imaging device in the clock-synchronized communication method, and receives, via the notification channel, the transmission request signal in the asynchronous communication method.
 12. The accessory device according to claim 1, wherein the accessory device comprises an imaging optical system capable of forming a subject image on an imaging device of the imaging apparatus.
 13. The accessory device according to claim 1, wherein the accessory control circuitry starts receiving of the second data after starting transmission of the first data.
 14. The accessory device according to claim 13, wherein the accessory control circuitry starts receiving of the second data after transmitting a start bit included in the first data.
 15. An imaging apparatus to which an accessory device is detachably mounted, the apparatus comprising: an imaging apparatus communication circuitry provided with, between itself and the accessory device, a notification channel used for notification from the imaging apparatus to the accessory device, an accessory data communication channel used for data transmission from the accessory device to the imaging apparatus, and an imaging apparatus data communication channel used for data transmission from the imaging apparatus to the accessory device; and an imaging apparatus control circuitry configured to control the imaging apparatus communication circuitry, wherein the imaging apparatus control circuitry transmits, via the notification channel, a transmission request signal to the accessory device, the transmission request signal being a signal for requesting data transmission from the accessory device to the imaging apparatus, and transmits a second data to the accessory device, via the imaging apparatus data communication channel, in response to starting to receive a first data transmitted, to the imaging apparatus, from the accessory device according to the transmission request signal.
 16. The imaging apparatus according to claim 15, wherein a period to receive the first data and a period to transmit the second data are partially overlapped.
 17. The imaging apparatus according to claim 15, wherein the imaging apparatus control circuitry starts transmitting the second data in response to reception of a start bit included in the first data.
 18. The imaging apparatus according to claim 15, wherein the imaging apparatus control circuitry transmits the transmission request signal to the accessory device by changing a voltage level of the notification channel.
 19. The imaging apparatus according to claim 18, wherein the imaging apparatus control circuitry transmits the transmission request signal by changing the voltage level of the notification channel from a first level to a second level which is different from the first level, and the imaging apparatus control circuitry receives a third data from the accessory device, via the accessory data communication channel, by maintaining the voltage of the notification channel at the second level during and after receiving the first data.
 20. The imaging apparatus according to claim 15, wherein the imaging apparatus performs communication with the accessory device by switching between a data format where data frames are transmitted without a communication standby period, and a data format where data frames are transmitted with a communication standby period.
 21. The imaging apparatus according to claim 20, wherein in a case the communication format, between itself and the accessory device, is the data format where data frames are transmitted with the communication standby period, a number of data which the imaging apparatus control circuitry transmitted to the accessory device before the communication standby period, and a number of data which the imaging apparatus control circuitry received from the accessory device before the communication standby period are the same number.
 22. The imaging apparatus according to claim 20, wherein the imaging apparatus control circuitry transmits the transmission request signal by changing the voltage level of the notification channel from a first level to a second level which is different from the first level, and the imaging apparatus control circuitry notifies the communication standby period to the accessory device by setting the voltage level of the notification channel to the first level.
 23. The imaging apparatus according to claim 15, wherein the imaging apparatus control circuitry performs an asynchronous communication with the accessory device.
 24. The imaging apparatus according to claim 15, wherein the imaging apparatus is communicable with the accessory device by switching communication methods between a clock-synchronized communication method synchronized with clock signals and an asynchronous communication method, and the imaging apparatus control circuitry transmits the clock signals to the accessory device, via the notification channel, in the clock-synchronized communication method, and transmits the transmission request signal to the accessory device, via the notification channel, in the asynchronous communication method.
 25. A non-transitory storage medium storing a communication control program for causing a computer of an accessory device, wherein the accessory device is detachably mounted to an imaging apparatus, the accessory device comprising, between itself and the imaging apparatus: a notification channel used for notification from the imaging apparatus to the accessory device; an accessory data communication channel used for data transmission from the accessory device to the imaging apparatus; and an imaging apparatus data communication channel used for data transmission from the imaging apparatus to the accessory device, wherein the communication control program causes the computer of the accessory device to perform the steps of: transmitting a first data to the imaging apparatus, via the accessory data communication channel, in response to receiving a transmission request signal, the transmission request signal being a signal for requesting data transmission from the accessory device to the imaging apparatus via the notification channel; and receiving a second data, via the imaging apparatus data communication channel, transmitted from the imaging apparatus in response to start receiving of the first data.
 26. A non-transitory storage medium storing a communication control program for causing a computer of an imaging apparatus, wherein an accessory device is detachably mounted to the imaging apparatus, the imaging apparatus comprising, between itself and the accessory device: a notification channel used for notification from the imaging apparatus to the accessory device; an accessory data communication channel used for data transmission from the accessory device to the imaging apparatus; and an imaging apparatus data communication channel used for data transmission from the imaging apparatus to the accessory device, wherein the communication control program causes the computer of the imaging apparatus to perform the steps of: transmitting a transmission request signal to the accessory device, via the notification channel, the transmission request signal being a signal for requesting transmission of data from the accessory device to the imaging apparatus; and in response to start receiving of a first data transmitted from the accessory device according to the transmission request signal, transmitting, a second data to the accessory device via the imaging apparatus data communication channel.
 27. An imaging system including an imaging apparatus and an accessory device detachably mountable to the imaging apparatus, wherein the accessory device comprises: an accessory communication circuitry having, between itself and the imaging apparatus, a notification channel used for notification from the imaging apparatus to the accessory device, an accessory data communication channel used for data transmission from the accessory device to the imaging apparatus and an imaging apparatus data communication channel used for data transmission from the imaging apparatus to the accessory device; and an accessory control circuitry configured to control the accessory communication circuitry, wherein the imaging apparatus comprises: an imaging apparatus communication circuitry having, between itself and the accessory device, the notification channel, the accessory data communication channel and the imaging apparatus data communication channel; and an imaging apparatus control circuitry configured to control the imaging apparatus communication circuitry, wherein the imaging apparatus control circuitry transmits a transmission request signal to the accessory device, via the notification channel, the transmission request signal being a signal for requesting data transmission from the accessory device to the imaging apparatus, the accessory control circuitry transmits a first data to the imaging apparatus, via the accessory data communication channel, in response to receiving the transmission request signal, and the imaging apparatus control circuitry transmits a second data to the accessory device, via the imaging apparatus data communication channel, in response to start receiving of the first data. 